Method of producing magnetic materials



Patented Ma 17, 1932,

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won or rnonucmemonnrrc m Draw1ng.- Application filed October 29, 1927, semi"'n o..22a,ao1. Renewed November- 20, 1931.

This invention relates to methods of producing magnetic materials, and more partlcularly to methods of producing brittle magnetic alloys for' use in 2 electrical r signaling Lg apparatus,such as cores for loading coils. employed in telephone circuits,

' The principal object of the invention 1s the production of a magnetic material, ing a fine crystalline structure, to facilitate .10 its reduction to a very finely divided ,form, and'possessing to a high degree those physi: cal electrical and magnetic properties which malre it highly desirable-in'electrical signaling. apparatus, especially in cores for loading ,1 coils for telephonecircuits. I

The magnetic material produced in accordance with the invention is of particular advantage in the production of magnet cores of the so-called r netic material isreduced to very finely divided particles, the particles treated to produce an insulatingc oating thereon and pressed into rings or cores. One method of 5 utilizing the finely divided magnetic mateinUnited States Patent No. 1,669,643, granted May 15, 192.8, to J. W.- Andrews and R. Gillis. However, the magneticmaterial is not limited in its use to the articular insulator disclosed in the foregoing application nor to any particular form of core but may be put to any use within the scope of the appended claims.

In accordance with one embodiment, the 3 present invention contemplates the production of brittle alloys of nickel and non by partially oxidizing the constituent, metals while in the molten state, working the metal in the solid state, while hot, to produce a fine crystalline structure and quenching the material to prevent crystalline growth. More specifically,'the invention contemplates the I productionof brittle nickel iron alloys, generally known as permalloy in which the proportions of its constituents are more than nickel and the remainder v principally iron, one form which has proven satisfactory having a nickel content which is approximately 80% of the whole. In this embodiment the constituents are havdust type in which a magrial to produce loading coil cores is described melted in-thepresence ofjoxygenand an oxidizing substance, the moltenj' material is boiled until it is oxidized, ispo'ured into a- "mold and allowed tosolidify; ,The solidified material. is then rolled while hot to produce a fine crystalline structure at such a rate that the materialreaches a temperature-slightly above that at which it ceases to be. malleableat about the same timethat the final reduction of the material is effected. After the material has been sub'ected to the above .described rolling operat quenched to lower the temperature of the material below the temperature of recrystallization in order to prevent crystal growth.

Methods of oxidizing. and working the metals constituting the alloy are disclosed in United States Patent No. 1,669,649, granted May 15,1928, to'C.1P. Beath and H. M. Heinicke and the c'opending joint application of C. P. Beath and H. M. E, Heinicke, Serial No. 229,790, filed October 29, 1927, but

, for the sake of completeness they will alsobe described in detail herein. o

One method of producing the brittle, fine ion it is immediately grained material in accordance with the in- A vention consists in placing. the required quantities of nickel and iron ina suitable furnace, preferably electrically heated, adding a calculated quantity of oxidized material of the same purity, and heating the ma-- terial until it is molten under oxidizing conditions'. Since, if virgin metal is used, it requires considerable time to obtain a melt which isoxidized to the right degree, oxidized material may added to furnish ad ditional oxygen to reduce the time consumed in completing the operation. Iron oxide in the form of iron ore may also be added to furnish oxygen-within the bath; When the material has become moltenit is oxidized by boiling for a length oftime determined by the amount of oxidation desired and the type of furnace used. The degree of oxidation of the material depends upon the length of;

the melting period, the length of the boiling exposed to the air, and the amount of 0 gen present in the charged material, and the eating and boiling periods are governed bythe period, the amount of the surface of the melt 46 product.

various charges and the type of furnace used. After the molten material has been oxidized to the required degree, it is then poured into an ingot mold, and as soon as the material is sol1dified,'the ingot is' removed and allowed to cool.

' Samples of the material are taken from various parts of'the ingot for analysis and if the material is of the required composition it is placed in a furnace where it is heated to approximately 1325" C., at which temperature it may be easily rolled. In order to 0btain a fine dust, the material should have a very fine crystalline structure which is 01) 1 tained by successively passing the hot 'billets from the heating furnace, without a subsequent reheating, through progressively reducing rolls at such a rate that the mate- .rial passes-through the final reducing roll at about the time that the material has cooled to a temperature slightly above that at which the material ceases to be malleable and immediately quenching the material to a tempera mm below its temperature of recrystallization. The uenching step may be performed in any of t e usual ways well known in the art, such as by conveying the materialdirectly from the final roll into a tank of water. The working of the metal breaks down 80 the large grained, crystalline'structure of the billet and produces a'very fine grained crystalline product which is extremely brittle, andsince the material is immediately quenched to a temperature below its temper- 3 ature of recrystallization after the final rollj ing operation. there is no opportunity for the crystals to grow in size after the quenching step and the resulting product has an extremely fine crystal structure. This is very 40 desirable because in this material the fracture takes place principally along the crystalline boundaries and consequently the smaller the size of the crystals the finerv the dust which can be produced from the finished Should the material become cooled while passing through the rolls to a temperature slightly above that at which it. ceases. to be malleable before the final roll is reached, the

Q rolling operation may be-stopped and the material reheated to a temperature at which '5 it becomes malleable and the-rolling operation continued provided, however, that the final rolling operation'is efiected as herein- I fore described at a temperature slightly greater than that at which the material loses its malleability.

. Instead of passing the material through reducing rolls during the entire time that it 00 is cooling, the material may be passed through only a few rolls, allowed to cool to a? temperature just'above that at which it'becomes non-malleable, then passed throu h an additional set of rolls and quenched. fine grained and easily pulverizable material will result from this treatment, but the dimensions of thepiece will differ from those of a piece produced by continuously rolling the material ,while it is cooling.

The material obtained by any of the above outlined operations is crushed in a jaw crusher, hammer mill, or an other suitable type of apparatus, after whic the crushed material 7 is reduced to a fine dust in a ball mill or any other suitable apparatus. The dust is sieved through a 120 mesh sieve and any residue is remelted and carried through the above operations to again reduce the material to a finely divided form.

By using an alloy of the proportions stated in the preceding paragraph and by following the foregoing method of procedure, a very fine grained crystalline product is obtained which is extremely brittle and whichwhen reduced to a fine dust yields a large percentage of particles which are small enough to pass through what is commonly known as a 200 v mesh sieve. When reduced to a finely divided form, the material is then in a form to be used for either continuous or lump loading of telephone circuits.

The finely divided magnetic materialobtained by the above described methods is particularly adapted tobe formed into rings or cores for loading coilsin any suitable manner. In one method which has proven satisfactory the finely dividcd particles are heated to a high temperature, are individually in' sulated by treating the particles in such a manner as to produce an insulating coating around each particle, the insulated material formed into rings 'or cores by the application of a high pressure, and. the rings annealed to stabilize the insulator and to give the rings the desired magnetic properties. A plurality of rings thus formed are then stacked coaxiallyto form a core on which the usual toroidal winding is applied, the number of such rings used depending upon the existing electrical characteristics of the telephone circuit with which the loading coils are to be associated. Since, in order to have low losses in loading coil cores made of permalloy dust in the above described man-. ner, it' is desirable that all of the material pass. through a 120 mesh sieve and a large percentage pass through a 200 mesh sieve, it is eadily seen that the material produced according .to this invention isespecially adapted to be usedin the production of such cores; By the statement employed hereinb'efore andin the annexed claims that; the final rolling of the. material is effected at atemperature slightly above that at which the material loses its malleability is meant that the materialreductions in the dimensions of the piece of material being worked upon may be produced by a rolling operation in which the piece remains intact.

What is claimed is a 1. A method of making magnetic materials,

which consistsv in heating the ing the magnetic material'at a-temperature above that at'which it ceases to be malleable,

at which the material reductions in the dimen sions thereof may be effected while the piece remains intact, and quenching the material.

material to a. temperature of approximately 1325 C.,work-,

, ing the alloy while hot until it"rea'ches a tem- Y perature sliggitly above that at which it ceases tov bemallea temperature below its ftalllzation. i I

In..witness whereof, I hereunto subscribe my name this 22nd day of October A. 1)., 1927.

. HERBERT MARTIN EDWARD HEINICKE.

a 4. A method of making brittle magnetic materials, which consists in heating a piece of a magnetic material to a temperature at which it becomes malleable, progressively reducing the cross-sectional dimensions of the piece at such a rate that the final reduction is effected at a temperature slightly greater than that at which the material ceases to be malleable,

and quenching to a lower temperature.

5. A -method of making fine crystalline structures from brittle magnetic materials, which consists in working the material at a temperature slightly above that at which it ceases to'be malleable, and quenching the material toalower temperature.

6. A method of making fine crystalline structures from brittle oxygenous magnetic.

alloys, which consists in heating the material to a temperature of approximately 1325 0., rolling the material while hot until it reaches a temperature slightly greater than that at which it ceases to be malleable, and quenching the material to a temperature below its tem perature of recrystallization.

7. A method of making fine crystalline structures from brittle magnetic alloys composed of more than25% nickel and the remainder principally iron, which consists in heating the material to a temperature of approximately 1325 C., rolling the alloy until it reaches a temperature'slightly above that at which it ceases to be malleable, and quenching the alloy to a lower temperature.

8. A method of making fine crystalline structures from brittle oxygenous magnetic materials in finely divided form composed of 80 parts of nickel and 20 parts of iron, which consists in heating the material to a;

temperature of approximately 1325 0., roll- I le, and quenching the alloy to a temperature of recrys 7 

